What is a dongle?

I see people asking if they could use a "dongle" with an iPad or iPad 2 WiFi (which I have). I did not understand the conversations, but I would like to know what is a dongle and if it might be of interest for me for my iPad 2.

A dongle is what the rest of the world calls an air card, wireless internet card. Its those little gizmos at the cell phone shops that look like think nub antennas. They are good for laptop that didn't come with a wireless internet card so that your laptop can either pick up wireless internet or support its own internet via its own data plan.